Selective scale formation

Abstract

A fluid stream is treated with at least one scale inducing agent prior to being passed through an engine having sweeping elements which limit the thickness of scale deposits therein to improve the efficiency with which the engine utilizes the energy contained within the fluid stream.

That which is claimed is: 
     
       1. A process comprising: treating a fluid stream to be passed through an engine having sweeping elements which limit the thickness of depositions of materials from the stream between the sweeping elements of the engine with at least one scale inducing agent so as to cause deposition of scale between the sweeping elements of the engine.   
     
     
       2. A process as in claim 1 wherein the fluid stream is comprised of heated brine and saturated steam. 
     
     
       3. A process as in claim 2 wherein said fluid stream is from a geothermal source. 
     
     
       4. A process as in claim 3 wherein said stream is treated with said at least one scale inducing agent prior to passing said fluid stream through said engine. 
     
     
       5. A process as in claim 4 further comprising treating said stream with at least one scale forming precursor prior to treating said stream with said scale inducing agent. 
     
     
       6. A process as in claim 4 wherein said stream contains at least one anion selected from the group consisting of carbonate, hydroxide, bicarbonate, sulfate, sulfide, borate, aluminate, silicate, nitrate and phosphate group containing anions and said scale inducing agent comprises a solution containing at least one cation selected from the group consisting of magnesium, silver, palladium, copper, nickel, zinc, arsenic, antimony, bismuth, tin, chromium, iron, cobalt, calcium, strontium, barium, lithium, rubidium, cesium, titanium, aluminum, nitronium, sulfonium, phosphonium and iron. 
     
     
       7. A process as in claim 4 wherein said stream contains at least one cation selected from the group consisting of magnesium, calcium, strontium, silver, palladium, copper, nickel, zinc, arsenic, antimony, bismuth, tin, chromium, iron, cobalt, barium, lithium, rubidium, cesium, titanium, aluminum, nitronium, sulfonium, phosphonium and iron and said scale inducing agent comprises a solution containing at least one anion selected from the group consisting of carbonate, hydroxide, bicarbonate, sulfate, sulfide, borate, aluminate, silicate, nitrate and phosphate group containing anions. 
     
     
       8. A process as in claim 5 wherein one of said scale forming precusor and scale inducing agent contains cations selected from the group consisting of magnesium, calcium, strontium, barium, lithium, rubidium, silver, palladium, copper, nickel, zinc, arsenic, antimony, bismuth, tin, chromium, iron, cobalt, cesium, titanium, aluminum, nitronium, sulfonium, phosphonium and iron and the other contains anions selected from the group consisting of carbonate, bicarbonate, hydroxide, sulfate, sulfide, borate, aluminate, silicate, nitrate and phosphate containing anions. 
     
     
       9. A process as in claim 4 wherein scale deposits containing calcium are formed in said engine. 
     
     
       10. A process as in claim 9 wherein the scale deposits formed in the engine also contain carbonates, sulfates, borates, aluminates, silicates sulfides and/or phosphates. 
     
     
       11. In a process comprising: (a) providing a stream of geothermally heated fluid;   (b) treating said stream with a scale inhibiting amount of a scale inhibiting agent to at least mitigate scale formation by the stream;   (c) passing said stream through an intermeshing plural rotor helical screw expander to cause rotation of an output shaft of said screw expander, said expander being designed to limit scale buildup within by the sweeping action of its plural rotors;   the improvement comprising:   (d) injecting a sufficient amount of at least one scale inducing agent into said stream to cause deposition of scale in said screw expander whereby scale is deposited in said screw expander.   
     
     
       12. A process as in claim 11 wherein said scale inhibiting agent is represented by the formula: ##STR7## wherein n is an integer of from 0 to 2, X and Y are independently selected from the group consisting of hydrogen and hydrocarbyl having from 1 to about 6 carbon atoms, each M is indpendently selected from the group consisting of hydrogen and cations which cause water solubility of the scale inhibiting agent, and R n  contains 6 or fewer nitrogen atoms and is selected from the group consisting of hydrogen, aliphatic, aryl, alkaryl, arakyl, alicyclic and: ##STR8## wherein m is an integer of from 1 to 10, and R 1  and R 2  are individually selected from the group consisting of hydrogen, alkyl groups containing from 1 to 6 carbon atoms, ##STR9## 
     
     
       13. A process as in claim 11 wherein said scale inhibiting agent is selected from the group consisting of: ##STR10## 
     
     
       14. A process as in claim 11 wherein said scale inhibiting agent is a water soluble compound selected from the group consisting of: ##STR11## wherein M is selected from the group of cations consisting of NH 4   + , K + , Li + , Na + , Rb + , Ce +  and Mg ++ . 
     
     
       15. A process as in claim 13 wherein said at least one scale inducing agent comprises a water soluble salt of a group IA metal. 
     
     
       16. A process as in claim 13 wherein the geothermally heated fluid stream contains at least one water soluble salt containing at least one metal cation selected from group IA and IIA metal cations and wherein said at least one scale inducing agent comprises a water soluble salt having an anionic portion which forms a precipitate with at least a portion of the group IA and group IIA metal cations in the stream. 
     
     
       17. A process as in claim 16 wherein the scale inducing agent is represented by the formula: ##STR12## wherein n is an integer of from 0 to 2, X and Y are independently selected from the group consisting of hydrogen and hydrocarbyl having from 1 to about 6 carbon atoms, each M is independently selected from the group consisting of hydrogen and cations which cause water solubility of the scale inhibiting agent, and R n  contains 6 or fewer nitrogen atoms and is selected from the group consisting of hydrogen, aliphatic, aryl, alkaryl, arakyl, alicyclic and ##STR13## wherein m is an integer of from 1 to 10, and R 1  and R 2  are individually selected from the group consisting of hydrogen, alkyl groups containing from 1 to 6 carbon atoms, ##STR14## 
     
     
       18. A process as in claim 13 wherein the scale inhibiting agent and the scale inducing agent comprise the same compound. 
     
     
       19. A process as in claim 15 wherein the scale inducing agent is injected into said stream immediately prior to passing the stream through the screw expander. 
     
     
       20. A process as in claim 19 wherein the scale inducing agent is selected from the group consisting of calcium chloride and its hydrates, calcium bromide and its hydrates, calcium iodide and its hydrates, calcium bicarbonate, calcium acetate and calcium nitrate. 
     
     
       21. A method comprising regulating the addition rate of a scale forming agent to a helical screw expander responsively to the efficiency at which the expander is operating. 
     
     
       22. A method as in claim 21 wherein a heated fluid containing said scale inducing agent is passed through said screw expander thereby losing a position of its enthalpy and a mechanical output from said screw expander is employed to generate electrical power. 
     
     
       23. A method as in claim 22 wherein the efficiency at which the expander is operating is calculated from the electrical power generated from the expander output and the pressure loss, temperature loss, and mass flow rate of the heated fluid passing through the expander. 
     
     
       24. A method as in claim 23 wherein the addition rate of scale forming agent is increased responsively to a decrease in expander efficiency. 
     
     
       25. A method as in claim 24 further comprising monitoring the heated fluid passing from the screw expander for scale products and adjusting the addition rate of scale forming agent to reduce the amount of scale products in the fluid passing from the screw expander. 
     
     
       26. A method comprising: (a) passing a stream of geothermally heated fluid through a plural rotor helical screw expander;   (b) generating a signal representative of the efficiency at which the expander utilizes the geothermally heated fluid;   (c) introducing at least one scale inducing agent into the fluid stream upstream of the expander to cause the deposition of scale in the expander and a change in the signal from a first value representative of a first efficiency to a second value representative of a second efficiency.   
     
     
       27. A method as in claim 26 wherein the signal at the first value is representative of the efficiency of the expander when it contains substantially no scale deposits and wherein the signal at the second value is representative of the efficiency of the expander when it contains optimal amounts of scale deposits. 
     
     
       28. A method as in claim 26 wherein the signal at the first value is representative of the efficiency of the expander when it contains less than optimal amounts of scale deposits and wherein the signal at the second value is representative of the efficiency of the expander when it contains optimal amounts of scale deposits. 
     
     
       29. A method as in claim 28 wherein the stream of geothermally heated fluid contains a scale inhibiting agent. 
     
     
       30. A method as in claim 29 wherein the second value is preselected and the first value is at a predetermined value below the second value. 
     
     
       31. A method as in claim 30 wherein the stream of geothermally heated fluid contains calcium ion at a concentration of between 1 and 50,000 parts per million by weight. 
     
     
       32. A method as in claim 30 wherein the stream of geothermally heated fluid contains calcium ion at a concentration of between about 5 and about 50 parts per million by weight. 
     
     
       33. A method as in claim 30 wherein the scale inducing agent is introduced into the stream of geothermally heated fluid so as to impart to the stream of geothermally heated fluid a concentration of scale forming agent of between about 0.01 and about 100,000 parts per million by weight. 
     
     
       34. A method as in claim 30 wherein the scale inducing agent is introduced into the stream of geothermally heated fluid so as to impart to the stream of geothermally heated fluid a concentration of scale inducing agent of between about 0.1 to about 1,000 parts per million by weight. 
     
     
       35. A method as in claim 32 wherein the scale inducing agent is introduced into the stream of geothermally heated fluid so as to impart to the stream of geothermally heated fluid a concentration of scale inducing agent between about 1 and 50 parts per million by weight. 
     
     
       36. A method as in claim 34 wherein the scale inducing agent comprises a water soluble calcium compound. 
     
     
       37. In an apparatus comprising: (a) an intermeshing plural rotor helical screw expander, and   (b) means for conveying a geothermally heated fluid stream from a geothermal source to the screw expander;   the improvement comprising:   (a) a container;   (b) a conduit establishing communication between the container and a point in the means for conveying a geothermally heated fluid stream which is immediately upstream of the screw expander; and   (c) means for pumping a fluid from the container and through the conduit.   
     
     
       38. Apparatus as in claim 37 further comprising a meanns cooperating with the conduit for controlling fluid flow through the conduit. 
     
     
       39. Apparatus as in claim 38 further comprising: (a) a second container;   (b) a second conduit establishing communication between the container and a point in the means for conveying a geothermally heated fluid stream which is upstream of the screw expander;   (c) means for pumping a fluid from the second container and through the second conduit; and   (d) a means cooperating with the second conduit for controlling fluid flow through the second conduit.   
     
     
       40. In an apparatus comprising: (a) an intermeshing plural rotor helical screw expander; and   (b) means for conveying a geothermally heated fluid stream from a geothermal source to the screw expander;   the improvement comprising:   a means for injecting at least one scale inducing agent into said fluid stream immediately upstream of said screw expander.   
     
     
       41. Apparatus as in claim 40 further comprising: a means for establishing a signal representative of the operating efficiency of the expander; and   a means cooperating with the means for injecting at least one scale inducing agent for controlling the rate of injection of scale inducing agent in response to said signal being representative of an efficiency lower than a preselected maximum efficiency.